Electromagnetic core construction



Jam 1' 1963 A. E. FEINBERG ETAL 3,071,744

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3,071,744 ELECTRMAGNETIC CGRE CONSTRUCTIN Albert E. Feinberg and Paul I. Zerwes, Chicago, Ill., as-

signors to Advance Transformer Co., Chicago, Ill., a corporation of Illinois Original application Dec. 14, 1954, Ser. N 475,043, now Patent No. 3,002,263, dated Get. 3, 1961. Divided and this application Dec. 19, 1957, Ser. No. 707,075

n 13 Claims. (Cl. 336- 212) This invention relates generally to a core construction for electromagnetic devices such as transformers, chokes and the like and in addition is concerned with a novel method of constructing a core of this type.

The invention is particularly applicable to shell type cores constructed of laminations and in which there is a generally rectangular outer frame or shell, having elongate sides and ends bridging the sides, and in addition there is a central winding leg which is disposed between the ends extending the length of the interior of the outer shell. Inpractice, a core of this structure is formed of a stack of laminations, each stamped out of silicon steel sheeting, held together by rivets or clamps. The difiiculties which will be referred to occur principally in 4the riveted coresbut are not exclusive thereto. In stamping kthe individual laminations, the central winding leg lamination is punched out of the blank simultaneously 'that the windows and outer frame portions are formed. This may occur in a progressive sequence, with the various parts separated by the punch press. Y Y

Thereafter, the frame laminations and winding leg laminations are separately stacked and riveted together. The air gap or gaps are formed during the punching operations, usually by a cutting operation known as shaving. This operation establishes the dimensions of the air gap or gaps, by means of which the eventual electrical characteristics ofthe device are established., The stacked winding leg is now provided with pre-wound coils that are slipped over the ends and positioned in alignment with the windows of the shell or frame stack',

4vand thereafter the assembled winding leg and coilsV are forced into the center ofv the frame or shell. Means are provided for positive alignment and seating ofthe central winding leg.

The above describes a method of producing the cores `which is in common use. The further processing of thedevice is not involved in this invention.

Theoretically, since the central leg is re-fitted back into the opening formed when it was punched out, there should be no problem in so assembling the transformery or choke.- Thus, predetermined gaps should knot vary for any reason. This is not the case, however. In any shearing die which includes male and female portions, there must be clearance no matter how little. The workpiece is therefore acted upon above and below by kshearing members which are moving along different parallel planes. A certain amount of cutting will take place,

depending upon the sharpness `of the die halves, but separation eventually occurs along a tear which extends.

diagonally from the contours defined by the male die portion to the contours defined by the female'die portion. Considering the definition of the resulting pieces by the contours of the male portion of the die; the punched out part will have an outward extension, and the perforated part will have an undercut.

Obviously, fitting a single thickness of a winding leg lamination to a single thicknessof a frame or shell Y lamination presents little or no problem. The aligned members are assembled in the direction opposite that in which they were separated during the punching operation. When a plurality of members are stacked, obviously there can be no nesting in assembling, since the United States Patent O f statutes relating thereto.

3,071,744 Patented Jan. 1, 1963 ICC largest contour of the one must pass the smallest contour of the other during the pressing-in process, resulting in either crushing of the edges or deformation of one part' or the other.

Since the stacked winding legs are engaged with the shells only at their ends, deformation which occurs duringthe pressing in of the central winding leg in practically all cases affects the bridging ends of the shell, bowing them outward. This results in distortion of the unsupported elongate side walls with resultant change in the gap dimensions. Thus the electrical characteristics of the device are changed resulting in unsatisfactory performance of the transformer or choke. Since die sharpness is an important factor and this varies, it is next to impossible to compensate for the change in gap thickness by, for example, shaving more material from gap forming extensions than necessary if there were no distortion.

It is the primary object of the invention to offset the above disadvantages otherwise inherent in the pressed-in shell type core structure, by preventingy distortion of the elongate sides of the core during the pressing-in of the winding leg. y

A further object of the invention lies in the provision of means on the bridging ends of the outer shell or frame of the core to prevent distortion of the elongate sides of the shells, and in connection with this object various means comprise weakened portions which will absorb or take on any distorting strain without transmitting the same to the sides.

A still further object of the invention lies in the provision of means on the central winding leg to accomplish .the elimination of distortion in the elongate sides, and

specifically the said means may consist of a formation shortening the length of said winding leg.

Still a further object of the invention lies in the proviison of a novel method for accomplishing the shortening of the central winding leg. y

Many other objects will occur to those skilled in the art as a description of the invention proceeds in which preferred embodiments of the invention have been described in some detail in order to comply'with the lpatent A preferredV embodiment of the method has also been described.

In the drawings:

FIG. 1 is a top plan view of a lamination for a shell type core showing the manner in which the -central winding leg portion matingly engages with the shell or frame portion and illustrating the conventional construction.

FIGS. 2 and 3 are diagrammatic views on a greatly enlarged scale showing in section what occurs in the punching operation during formation of the lamination of FlG. l.

FIG. 4 is an enlarged and exaggerated sectional view showing the formation resulting along the edges of the parts of the lamination of FIG. l as a result of the punching operation.

FIGS. 5 and 6 are fragmentary plan views of the right hand ends of laminations formed in accordance with the invention to eliminate distortion of the sides of the shell core during the pressing-in operation.

FIG. 7 is a fragmentary plan view of the left hand end of another lamination formed in accordance with the invention and illustrating a third form.

FIGS. 8 and 9 illustrate steps in the formation of the lamination ofiFIG. l0, the latter illustrating a fourth t 'tion of the die. vthe workpiece preparatory to being pressed upon the same `70 that exceeds the tensile strength of the material.

ing the growing of the winding leg laminations during punching. In order to obtain a clear picture of the problems solved attention is invited to FIGS. l through 4.

FIG. l illustrates a lamination 2t) having a shell or frame part 21 of rectangular construction, and a central winding leg portion 22 which is punched out of the same blank forming the lamination 20, with its ends matingly engaged at 24 and 26 with the bridging ends 2S and 30 respectively of the frame part 21. The sides are designated 32 and 34. Windows 36 and 3S are formed between the winding leg part 22 and the frame part 2li for the reception of the coils (not shown)- The windows are separated by juxtaposed spaced apart extensions 40 and 42 on the frame part 21 extending inwardly toward the outwardly extending counterparts 44 and 46 on the winding leg part 22. The separation forms the gaps 48 and Sti the spacing of which is critical in most electromagnetic devices, since the reluctance of the shunt (that is the combined extensionsrand gaps) affects the reactive rela- Y tionship between` the coilsin the respective windows.

The contours of the lamination 20 are identical to the contours of the transformer which is manufactured from a plurality of such laminations. Only the windings and fastening means are not shown. Thus, a predetermined number of parts 21 are stacked together in perfect alignment through the assistance of an indexing notch 52 on an Yedge of the side 34, and riveted together. Rivet holes are shown at 54. The same number of parts 22 are also stacked together and riveted, the rivet holes being shown at 56. An indexing hole part of which is in the bridging end 3d and part of which is in the end of the winding leg part 22, serves the dual purpose of enabling leg into the frame is easily ascertained by reason of the ,bui-rs on both parts.

The smooth surface of the winding leg stack is to be inserted into the burrcd side of the frame part stack.

As described thus far, the construction is conventional Vand the manner of inserting the winding leg in the core is well-known. This method of assembly gives rise to distortion of'the sides 32 and 34 with attendant changes in the width of gaps 48 and 50.

In FIG. 2 there is illustrated a blank or workpiece 60 from which the lamination 20 is to be punched. For the sake of description, it will be presumed that the diagram illustrates in exaggerated dimension, the formation of the mating junction 24. The workpiece 60 is shown upon a lower die part 61 which has therein an opening 62, of the configuration of the Winding leg part 22 (either with or without the windows). This is then the female por- The punch 64 is shown poised over and driven into the opening 62. Obviously, it has the same contours as the opening 62, but must be slightly smaller to permit such downward movement. The clearance between die parts 61 and 64 is represented by the space 66. Y

As the male die part 64 is driven downward, the sharp edges 68 and 70 at first bite into the workpiece 60, giving rise to pure shear surfaces 72 and 74. This pure shear continues until the movement of the separating parts of the workpiece 60 produces a stress across the edges 63 and At this point the material yields, tearing across this diagonal along the line '76. The exact position of this tear surface (it is actually a surface formed about the edges of both of the separated pieces) depends upon many factors among which are: tensile strength of the steel, clear: ance 66 of the die parts, thickness of the workpiece 60,

sharpness of the dies, type of workpiece padding, etc.V

The resulting pieces are illustrated in FIG. 4, forming the rbridging endZt and the .end of the central leg part 22.

part 21 is smaller than the contour of the winding leg 22 defined by the edge 74. Certainly the greatest distance between the mating junction 24-26 of the frame part 21 K is substantially less than the greatest distance between the ends of the winding leg part 74. When a stack of winding leg laminations is forced into the center of the frame something must give. l

It has been found that the bridging ends 28 and 30 tend to bow outward when the winding leg stack is pressed home. This is illustrated in exaggerated form by the broken lines and 82 in FIG. l. The resulting distortion of the stacked frame laminations is usually an inward bowing of the elongate sides. This is exaggeratedly illustrated by the broken lines 84 and 86. The inward lbowing of thesides 32 and 34 of the frame stack will materially decrease the width across gaps 48 and 50, and as explained, the amount of change of the gaps will not be controllable. Material changes in electrical characteristics of the transformer or choke over original design will result from this alteration in gap dimension. may in some way olfset this change, but the forces applied are great and some change is bound to result notwithstanding. l

In any event, electrical changes result from such distortion which in many cases are intolerable. The ,dilif culties are aggravated where a close tolerance of gaps is its growing Y In FIGS. 5 and 6, means are provided in the bridging end 30 capable of absorbing deformation. Y In the lamination 120 of FIG. 5 there is a series of slots 90'which are i i i punched completely through the bridging endand generally are arrangedat right angles to the forces exerted ,i

when the winding leg 22 is driven into place. Thus the s lots are in an arc about the junction 26. The slots provide a weakened portion in the bridging end which will be somewhat crushed, perhaps slightly closing the slots when the winding leg is pressed home. Obviously if the distortion is all localized in the bridging end 30, there will be no distortion or bowing inward of the sides 32 and 34 andthe gaps 48 and 50 will be unaffected. i

In the lamination 220 of FIG. 6, the slots 91 serve the same function as slots 90, but these are arranged geometrically different. A greater amount of weakening is provided at local areas adjacent the inner corners ofthe end member 30. The function and operation Vis the same as slots 90.

In slotting the end 3l), care must be taken to provide sufficient iron to handle the normal flux designed to threadY the core. Note that Vthe width of the end 30 is larger in FIGS.,5 and 6 thanV in FIG. l for the same design of eleci tromagnetic device. Obviously the slotting decreases the cross section in places. The exact number and formation of .slots is a matter of design, probably best ascertained by experiment, especially in view of the complex nature of the electrical characteristics of this kind of apparatus. Care must be taken to avoid any areas whereextreme;

high flux density may result in saturation.

In the lamination 32u illustrated in FIG. 7, instead of i slotting the end 23, a shallow recess or notch 93 is formed Gap materials i In a second form, the winding leg is shortenedlslightly during manufacture to compensate for alongthe outer edge of the end, so that when distortion occurs as it might in forcing the winding leg home, the narrow strip .94 between the juncture 24 and the recess 93 will tend to bow out or ilex as indicated at 95 rather than the entire bridging end 28. The same salutary effects are obtained as in FIGS. 5 and 6.

In FIG. there is illustrated a lamination 420 in which the construction is identical to that of the lamination 10 of FIG. l with one exception. There is a crimp 97 of simple formation which extends across the'central winding leg part 2K2 at the extensions 44 and 46. The crimp may be of vany configuration 30 that a stack of members 22 will nest,

one such formation being triangular in cross section as shown in FIG. ll. Obviously the crimp 97 will shorten the length of the winding leg 22`slightly, and thereby offset the growth thereof during stamping. This can prevent the distortion of the ends 28 and 30 during assembly of stacks. Obviously there mustbe no crimp in the frame portion 21.

The crimp may be formed in the lamination 22 in any of a variety of ways and at any of the stages in the punching of the lamination, but for high speed production, a

novel method of forming said crimp has been evolved. During the production'of the lamination, at any suitable stage of the stamping operation, sayL during thev first blanking step, oreven before blanking, if desired, the entire lamination is crimped across the position of the shiint, `that is, at the extensions 40, 42, 44 and 46. The crimp is more easily formed in a large and imperforate member. Thereafter, the crimps 97' in the sides 32 and 34 are fiattened. The nal result will be the same as FIG. l0. The

illustration in FIG. 8 shows theA lamination assembled together prior to the flattening of the frame part 21. Obviously before this occurs, the winding leg part 22 drops out of the press so that FIG. 9 illustrates the result of the flattening step. By illustrating both parts 21 and 22 in FIG. 8 it isfnot intended to imply that the entire lamination is completely punched to shape before the crimps 97 and 97 are formed (although this might be done). Preferablythe crimping should be done at a stage of the progressive punching process at` which there will be a minimum of distortion of the extensions forming the shunt and` gaps..

The only reason for the crimp 97 being where shown in FIG. l0 is that it interferes least with the insertion of the stacked windingfleg into the coils from opposite ends. The crimp 97 will,l however, be quite small, and may be located in other places along the member 22 where convenience and practicability permit. `Obviously there may be several crimps, if desired. v

What it is desired to secure by Letter Patent of the United States is:

1. An krelectromagnetic core constructionof the shell type comprising an integral Vsubstantiallyrectangular outer shell having elongate sides and continuous bridging endparts `connecting said sides, a central winding leg installed on the interiorof the shell extending the length of said interior and having each end face'thereof disposed iiiV intimate engagement with a said end part, said elon- V,gate sides and winding leg having extensions thereof Aon oppositesides of the'winding leg and alignedto provide located to absorb forces exerted during said assembly capable of causing such change and distortion.

2. A core construction as described in claim l in which said means is provided in the said winding lega 3. A core construction as described in claim l in which said means is provided in the said winding leg, comprising a crimp in said leg extending transversely of the leg at said extensions.

4. A core construction as described in claim l in which said means is provided in a said bridging end.

5. An electromagnetic core construction of the shell type comprising, an integral substantially rectangularouter shell having substantially parallel elongate sides .and

continuous bridging end parts connecting said sides, a central winding leg on the interior of the shell extending the length of said interior and having each end face thereof intimately abutting a said end part, said shell and winding leg each comprised of a stacked assembly of individual electrical steel stampings of which the winding leg stampings each has a physical length and end face contour cornplementary with the distance between bridging end parts and `the contour of a lateral edge of each shell stamping such that each winding leg stamping is capable of being lstamped from a shell stamping, and means provided on said` bridging end parts preventing distortion of said elongate Sides notwithstanding inherent discrepancies in dimensions and contours of individual winding leg and shell stampings capable of effecting such distortion when the stampings are stacked and assembled to form said core, said means comprising at least one of .said bridging end parts having a cut-out formation located with respect to the abutting juncture of a said end face and end part to absorb deformation normally arising during such assembly. y

6. A core construction as described inclaim 5in which said cut-out formation is provided in a lateral surface of said one bridging end part and said one bridging end part has its opposite lateral surface engaged with a said end face. 7. yA core construction as described in claim 5 in which said cut-out formation comprises at least one recess formed in an edge of said one bridging end part opposite a .second edge of said end part engaged with a said end face.

8. A core construction as described in claim 5 in which said cut-out formation is provided in the lateral surface of said one bridging part and comprises notch means extending inwardly of the bridging part and thereby decreasing the lateral thickness of the said part.

9. A core construction as described in claim 8 in which said notch means includes two inwardly extending cuts spaced apart a distance greater than the depth of said cuts, and there being portions of said surface indented between said cuts whereby to provide said decreased lateral thickness between thecuts of .said notch means.

air gaps of predetermined dimension between end faces of aligned extensions, said shell and winding leg each comprising a stacked assembly of individual electrical steel vstampings of which each winding leg stamping has been stamped from a said shell stamping, and means for simultaneouslypreventingchange in the predetermined dimension of the air gaps and preventing the distortion of said elongate sides notwithstanding inherent discrepencies in the dimensions of individual winding leg and shell stampings capable of causing such change and distortion when'the stampings are stacked and assembled to form said core,V said means being provided on one of said elongateleg and shell components advantageously l0. An electromagnetic core construction of the shell type comprising, a substantially rectangular outer shell having elongate sides and ends bridging said sides and a central winding leg installed on the interior of the shell between said ends extending the length of said interior and having each end face thereofV frictionally engagedv against a said bridging end, said elongatesides and winding leg having extensions thereof on opposite sides of the winding leg and aligned to provide air gaps of predetermined dimension between end faces of aligned extensions,

said shell and winding leg each comprising a stacked as-v sembly of individual electrical steel stampings, each winding leg stamping being struck from a said shell stamp- Y ing, and means for preventing change in the predetermined dimension of the air gaps to alter the desired electrical characteristics of the electromagnetic device for which the core construction is used resulting from said predetermined dimension of the air gap when the central winding leg is installed on into the interior of the shell, and said means is provided in a said bridging end, comprising weakened portions formed in said Yend capable of ab- `sorbing deformation thereof normally arising when the ltensions, said shell and winding leg each comprising a stacked assembly of individual electrical steel stampings, each winding leg stamping being struck from a said shell stamping, and means for preventing change in the prede termined dimension of the air gaps to alter the desired electrical characteristics of the electromagnetic device for which the core construction is-used resulting from said predetermined dimension of the air gap when the central winding leg is installed on into the interior of the shell, and said means is provided in a said bridging end, coniprising weakened portions formed in said end capable of absorbing deformation thereof normally arising when the winding leg is so forced into the shell, comprising a plurality of perforations extending through said bridging end and arranged in an are about the junction between the winding leg and said bridging end,

l2. An electromagnetic core construction of the shell type comprising, a substantially` rectangular outer shell having elongate sides and ends bridging said sides and a eachwinding leg stamping being struck from a said shellV stamping, and means for preventing change in the prede termined dimension of the air gaps to alter the desired winding leg is'installed on into the interior of the shell,y and said means is provided in a said bridging end, corn-` i prising weakened portions formed in said end` capable type comprising, a substantially rectangular outer shell having elongate sides and ends bridging said sides and a central winding leg installed on the interior of the shell between Vsaid ends extending the length of said interior and having each end face thereof frictionally engaged against a said bridging end, said elongate sides and wind ing leg having extensions thereof on opposite sides of the `winding leg and aligned to provide air gaps of predetermined dimension between end faces of aligned extensions, said shell and winding leg each comprising a stacked assembly of individual electrical steel stampings, each winding leg stamping being struck from a said shell stamping,

Y Velectrical characteristics of the electromagnetic Vdevice for 1 which the core yconstruction is used resulting from said -predetermined dimension of the air gap when the central and means for preventing change in the predetermined dimension of the air gaps to alter the desired electrical characteristics of the ,electromagnetic device for whichV r the core construction is used resulting from said prede-` termined dimension of the air gap when thecentral winding leg is installed on into the interior of the shell, and said means is providedtin a said bridging end,-comprising weakened portions formed in said end capable of `absorbing deformation thereof normally arising when the winding leg is so forced into the shell, comprising a recess formed in the edge of said bridging end removed from the junction of the winding leg and said bridging end. i i

References Cited in lthe tile of this patent UNITED STATES PATENTS 2,209,811 Dielstein V. July 30, 1940 2,346,621 4,Sola Apr. 11, 13944 2,509,187 Feinberg May 23; 1950 2,671,951 Sliwiak Mar. 16, 1954 2,713,666 Henderson V July 19,1955` 2,725,616 Epstein Q g v Deo. 6, 1955 Feinberg jl'uly` 24, 19,56 

1. AN ELECTROMAGNETIC CORE CONSTRUCTION OF THE SHELL TYPE COMPRISING AN INTEGRAL SUBSTANTIALLY RECTANGULAR OUTER SHELL HAVING ELONGATE SIDES AND CONTINUOUS BRIDGING END PARTS CONNECTING SAID SIDES, A CENTRAL WINDING LEG INSTALLED ON THE INTERIOR OF THE SHELL EXTENDING THE LENGTH OF SAID INTERIOR AND HAVING EACH END FACE THEREOF DISPOSED IN INTIMATE ENGAGEMENT WITH A SAID END PART, SAID ELONGATE SIDES AND WINDING LEG HAVING EXTENSIONS THEREOF ON OPPOSITE SIDES OF THE WINDING LEG AND ALIGNED TO PROVIDE AIR GAPS OF PREDETERMINED DIMENSION BETWEEN END FACES OF ALIGNED EXTENSIONS, SAID SHELL AND WINDING LEG EACH COMPRISING A STACKED ASSEMBLY OF INDIVIDUAL ELECTRICAL STEEL STAMPINGS OF WHICH EACH WINDING LEG STAMPING HAS BEEN STAMPED FROM A SAID SHELL STAMPING, AND MEANS FOR SIMULTANEOUSLY PREVENTING CHANGE IN THE PREDETERMINED DIMENSION OF THE AIR GAPS AND PREVENTING THE DISTORTION OF SAID ELONGATE SIDES NOTWITHSTANDING INHERENT DISCREPANCIES IN THE DIMENSIONS OF INDIVIDUAL WINDING LEG AND SHELL STAMPINGS CAPABLE OF CAUSING SUCH CHANGE AND DISTORTION WHEN THE STAMPINGS ARE STACKED AND ASSEMBLED TO FORM SAID CORE, SAID MEANS BEING PROVIDED ON ONE OF SAID ELONGATE LEG AND SHELL COMPONENTS ADVANTAGEOUSLY LOCATED TO ABSORB FORCES EXERTED DURING SAID ASSEMBLY CAPABLE OF CAUSING SUCH CHANGE AND DISTORTION. 